The present invention relates to a thyristor with a semiconductor body having at least four zones of alternate conductivity types, of which the first forms a main emitter and the second a base, with a control electrode connected to the base, and a first auxiliary emitter located between the main emitter and the control electrode, and with a second auxiliary emitter located between the first auxiliary emitter and the main emitter. Thyristors of this type have already been described with the aforementioned base and the other zones of the thyristor. The two auxiliary emitters form a structure serving to amplify the ignition current for the main thyristor, the main thyristor consisting of the main emitter, the aforementioned base, and the other zones of the semiconductor body. By means of this arrangement, it is possible to keep low the outlay for the control current source and, at the same time, insure a reliable ignition of the main thyristor by high control current.
Power thyristors are often provided with circuits featuring capacitors which are intended to attenuate voltage peaks. When the thyristor ignites, the capacitor discharges the currents, and high currents having current gradients of up to more than 1000 A/.mu. s are formed. Such extreme loads can themselves occasion the destruction of the first auxiliary thyristor.
A semiconductor thyristor having a main emitter and first and second auxiliary emitters is described in the German application laid open for public inspection, No. 1,589,455. In this disclosure, the first auxiliary thyristor is always ignited first, followed by ignition of the second auxiliary emitter, and finally ignition of the main emitter. The first and second auxiliary thyristors each provide control current amplification gain of approximately 10. Thus, a control current amplification is achieved, which is the product of the two auxiliary thyristors, namely, a control current amplification gain in the order of 100 times.